ULTRA LIGHT BOSONIC DARK MATTER AND COSMIC MICROWAVE BACKGROUND

Abstract

In this paper, we consider the hypothesis in which a species of ultra light bosonic dark matter (ULBDM) with mass mB ∼ 10−22 eV could be the dominant dark matter (DM) in the universe. As a first approach we work in the context of kinetic theory, where ULBDM is described by the phase space distribution function whose dynamics is dictated by the Boltzmann–Einstein equations. We investigate the effects that this kind of DM imprints in the acoustic peaks of the cosmic microwave background. We find that the effect of the Bose–Einstein statistics is small, albeit perceptible, and is equivalent to an increase of non-relativistic matter. It is stressed that in this approach, the mass-to-temperature ratio necessary for ULBDM to be a plausible DM candidate is about five orders of magnitude. We show that reionization is also necessary and we address a range of consistent values for this model. We find that the temperature of ULBDM is below the critical value implying that Bose–Einstein condensation is inherent to the ULBDM paradigm.